The present invention relates to a method and apparatus for settlement of accounts by IC cards which are used as prepaid cards or credit cards.
For instance, in an IC card which is used as a prepaid card, there is written the amount of money paid for its purchase, and before or after receiving a service the card user inserts the IC card into an IC card terminal, wherein the remaining value after subtracting the charge for the service from the initial value is transmitted to and written into the IC card.
In a conventional system of this kind, the IC card and the IC card terminal use the same cipher system and have the same secret key and communicate to each other the balance information enciphered by the common secret key. The IC card and IC card terminal are designed so that such a secret key cannot be found nor can it be altered even if the IC card terminal should be revealed to an outsider.
On the other hand, in the case of an IC card for use as a credit card, its identification number and other necessary information are preregistered and the user is allowed to receive his desired service when inserting the IC card into an IC card terminal and is charged for the service afterward. In a conventional IC credit card system, upon insertion of the IC card into the IC card terminal, the latter is connected online to a management center where IC card identification numbers and other user information are registered, then the user inputs his registration number and other required information by dialing, the thus input information is sent to the management center, wherein the user information registered in advance is used to verify the validity of the user. After the user's validity is thus proved, the user is allowed to receive his or her desired service at the IC card terminal.
Such an IC credit card system similarly adopts, with a view to providing increased security, a method in which: the IC card and the IC card terminal use the same cryptographic scheme and have the same secret key and they each authenticate the other's validity; a password input into the IC terminal is checked with its counterpart prestored in the IC card; the IC card identification number read out of the IC card is sent from the IC card terminal to the management center which has a data base of identification numbers and other information of IC cards; the IC card identification number is verified in the management center; the result of the verification is transmitted to the IC card terminal; and when the IC card identification thus checked in the management center is valid, the service specified by the card user starts through the IC card terminal. In some cases, the IC card and the management center each authenticate the other's validity directly through use of the same secret key.
The conventional methods mentioned above all call for communication between the management center and the IC card terminal and online processing for verification before or after the service is provided, and hence they have shortcomings that the management center facility is inevitably large-scale and that the charge for the service includes communication expenses. Moreover, the history of service can be stored in the management center or IC card but difficulty is encountered in proving that the stored contents are not false. Although it is almost impossible to falsify the stored contents of the IC card unless the secret key is let out, the secret key information in the IC card or IC card terminal is not perfectly protected and may in some cases leak out over a long time. In the case where the cryptographic scheme used is broken by third parties and many IC terminals are used by them, particularly in the event that IC cards and IC terminals are abused by unauthorized persons over a wide range, it is very difficult to change all of the secret keys at the same time--this poses a serious social problem as well-intentioned users cannot use their IC cards for a long period of time, for instance.